Method and electrode for defining and replicating structures in conducting materials

ABSTRACT

The present invention concerns an electrochemical pattern replication method, ECPR, and a construction of a conductive electrode for production of applications involving micro and nano structures. An etching or plating pattern, which is defined by a conductive electrode, a master electrode, is replicated on an electrically conductive material, a substrate. The master electrode is put in close contact with the substrate and the etching/plating pattern is directly transferred onto the substrate by using a contact etching/plating process. The contact etching/plating process is performed in local etching/plating cells, that are formed in closed or open cavities between the master electrode and the substrate.

TECHNICAL FIELD

The present invention relates to a new etching or plating method forsimplifying production of applications involving micro and nanostructures by using a special electrode, according to the appendedclaims.

The present invention is closely related to electrochemical etching,plating, photolithography and pattern replication and is within themicro- and nanotechnic area.

The method is particularly useful for fabrication of PWB (printed wiringboards), PCB (printed circuit boards), MEMS (micro electro mechanicalsystems), sensors, flat panel display, magnetic and optical storagedevices. Integrated circuits, different types of structures inconductive polymers, structures in semiconductors, structures in metals,and others are possible to produce using this method. Even 3D-structuresin silicon, by using formation of porous silicon, are possible.

BACKGROUND OF THE INVENTION

The ever-increasing demand for smaller, faster and less expensivemicroelectronic and micro-electromechanical systems requirescorresponding development of efficient and suitable manufacturingtechniques.

Either additive or subtractive techniques are used in the fabrication ofmicro- and/or nano-structures on a surface. One general subtractivetechnique is etching and one general additive technique is plating.

The etching methods are usually divided into two subgroups, dry- and wetetching. In general, dry etching is used for submicron structures and/orwhere straight sidewalls are important. Wet etching is used for largestructures where some undercutting is acceptable or sometimes desirable.The wet etching techniques can be divided into chemical- andelectrochemical etching.

The advantage of dry etching compared to wet etching is that anisotropicetched profiles can be generated in both crystalline andpolycrystalline/amorphous material. Some of the disadvantages of dryetching are high equipment costs, lack of selectivity, problems withre-deposition on the sample, environmentally hazardous chemicals,surface damages on the etched sample and safety and disposal problems.

The advantage of wet etching is that it is a simple and inexpensiveprocess. One of the disadvantages is that it does not involve anydirectional driving force and therefore the etching rate is the same inall directions, which results in an isotropic etch profile. Some otherdisadvantages are that wet etching baths generally contain aggressiveand toxic chemicals, which results in safety and disposal problems. Inmany wet etching processes waste treatment and disposal costs oftensurpass actual etching costs, and the same drawback applies for dryetching.

Detailed descriptions regarding the above mentioned etching processesare considered known by a man skilled in the art and will not bepresented in this paper. Because of the close relationship between theetching method according to the present invention and theelectrochemical etching some details regarding the later will bepresented as follows.

Electrochemical etching is a simple and inexpensive etching method,which makes it possible to achieve high etch rates and accurate processcontrol. In electrochemical etching an external electrical potential isapplied between an etched sample and a counter electrode, all immersedin a liquid etchant. An electrochemical cell with the working electrode,the sample, as anode and the counter electrode as cathode are formed, asshown in FIG. 1. An external potential is applied to drive the oxidationprocess at the working electrode. The corresponding reduction at thecathode is usually hydrogen gas formation. As electrolyte, and etchant,neutral salt solutions or very diluted mixtures of conventional etchantcan be used. The applied potential and the electric field from it give adirectional etching in the vertical direction.

One problem the designers of electrochemical etching cells are facing isthat, to reduce the resistive losses from charge transfer in theelectrolyte, one wants a small electrode distance. A small distance,which makes just a tiny unevenness in the electrode, give rise to arelatively big Δd that, gives a non-uniform current densitydistribution. The result is that some parts of the sample areover-etched while some parts are not etched to the desired depth. Nomechanical support is possible to keep the electrode in position overthe whole surface, since no contact between sample and counter electrodeis allowed.

Another problem in electrochemical etching is non-uniform currentdensity distribution arising from accumulated currents from non-etchedareas, due to the fact that all parts of the counter electrode are incontact with the electrolyte, and not only the desired areas above theetched parts.

The second option, additive techniques, for pattern transfer is to addmaterial in the structure formed on top of the substrate by thepattern-defining step. Electrochemical deposition, for which the personsskilled in the art also use the term “electroplating”, physical vapourdeposition and chemical vapour deposition are examples of additiveprocesses. It is known in the field that, by using electroplating, welldefined patterns, vertical sidewalls and high aspect ratio structurescan be fabricated. However, common industrial problems are associatedwith the known electroplating process, namely non uniform currentdensity distribution resulting in a deposition rate depending on thepattern surrounding each structure that is plated. Furthermore, suchdifferences in current density also result in different materialcomposition when plating alloys, as well as differences in height ofelectroplated structures on a substrate. Up to now, these undesireduneven distributions typically have to be rectified using planarizationmethods in a subsequent process step.

When the purpose of etching is to provide a structure in the etchingmaterial by etching away selected parts thereof, the etching materialwhich is not to be etched away is usually coated with an etchingpreventing layer, a so called mask or resist. The primary technique todefine patterns to be etched is photolithography and a common etchingpreventing layer is a photo-resist. The photo-resist is exposed byelectromagnetic radiation and developed to transfer the pattern whereetching is wanted. Every sample that is etched has to be coated withresist, pre-baked, exposed, developed and hard-baked before the etchingprocess can start.

Most of today's-micro-devices are built up by a large number offunctional layers and each layer has to be patterned and aligned in aphotolithography process followed by a pattern transfer process. FIG. 6shows a conventional etching process with the lithography process. Thecomplicated nature of the pattern defining lithography process and thelarge number of lithography steps needed to fabricate a micro-devicemakes it to a major time and cost carrier in the total manufacturingchain.

From the European patent publication EP 1060299 it is known to use amethod of making, by etching, depressions in selected portions of anetching surface by using an electrode with electrically conductiveelectrode portions in selected portions of an electrode surface, wherethe electrode portions is forming an electrode pattern which correspondsto the etching pattern. The method is different compared to the presentinvention by using electromagnetic radiation to dissolve a passivatinglayer, which is formed on the etching material. During etching theelectrode is placed at a distance from the electrically conductiveetching material, which also differs from the present invention. Theelectrodes according to EP 1060299 have to be transparent toelectromagnetic radiation and they do not compensate for unevenness inthe micro/nano areas.

WO 9845504 discloses a method for electroplating using an electroplatingarticle, an anode and a substrate. The electroplating article is put incontact with the substrate. In one embodiment, the external anode isplaced separated from the substrate and the electroplating article, allimmersed in an electrolyte. According to the disclosure, a potential isapplied over the external anode and the substrate, resulting in materialtransferred from the anode, through the porous carrier of theelectroplating article and plated on the substrate in a pattern definedby the insulating mask of the electroplating article. The electrolytevolume between the electroplating article and the anode can be agitatedto improve mass transfer of electroactive ions. However, the disclosedmethod struggles with the same problems and drawbacks as associated withconventional electroplating, namely non-uniform plating rates as aresult of non-uniform current density distribution due to the anodehaving areas with a surface size differing from the surface size ofcorresponding cathode areas on the patterned substrate. Thus,differences in reaction rates in different cavities result in platedmicrostructures with different heights depending on the patternsurrounding each structure. The problem is usually solved by asubsequent planarization process step like lapping or CMP (ChemicalMechanical Polishing). When plating alloys, the method described inWO9845504 suffers from the same problems as conventional platingprocesses, namely differences in material composition because of nonuniform current density distribution.

Furthermore, the mentioned embodiment disclosed in WO 9845504 requiresan electroplating article fabricated with a porous material that ispermeable for ions in the electrolyte, which gives rise to limitationsin how small dimensions that can be defined, depending on the pore sizeof the material.

In a second embodiment disclosed in WO 9845504 it is mentioned anelectroplating article that consists of a patterned mask placed onto ananode. The anode can be soluble or insoluble and can include an erodablelayer. In the method using a soluble anode, the material is transferredfrom the anode material in the electroplating article, thus theelectroplating article is eroded during use, but can be periodicallyredressed and reused. However, the problem of non uniform currentdensity distribution also applies to this method, as the patterned maskstill is placed as a separate layer onto the anode layer, i.e. thecurrent density distribution is only at the beginning of a platingprocess uniform, whereas the contact surface of the electrolyte with theanode material increases differently in each local plating cell,depending on its size, as anode material is consumed. Moreover, themaximum aspect ratio, i.e. height/width ratio, of structures that can beplated is limited by the fact that the erosion of the anode material inthe electroplating article undercuts the insulating pattern mask.Undercutting the mask layer during use is also associated withreliability problems, since the patterned mask layer will be completelyundercut and disintegrated from the electroplating article if theelectroplating process is not terminated in time. The problems describedare inherently associated with the method because the soluble anodicmaterial is transferred directly from the electroplating article itself,even in the case where the electroplating article consists of differentlayers of soluble and insoluble material.

SUMMARY OF THE INVENTION

One object of the present invention is to simplify production ofapplications involving micro and nano structures where an etching orplating pattern, which is defined by a conductive electrode, a masterelectrode, is replicated on an electrically conductive material, asubstrate. Also, the master electrode should be possible to reuse manytimes to fabricate replicas according to the method. More specifically,an object of the invention is to avoid unnecessary process steps, suchas the above mentioned planarization process steps, during saidproduction of said structures, and to enable an accurately controlledelectrochemical etching or plating process without limitations inmaximum aspect ratio of deposited structures, variations in materialcomposition of deposits and reliability problems in large scaleproduction.

Generally, this object is met by a special contact electrochemicaletching/plating method that is called the electrochemical patternreplication method. To simplify the description of the electrochemicalpattern replication method according to the present invention it isstated as the “ECPR” method further in this description. This method isbased on a structured electrode device, an electrochemicaletching/plating method, and an apparatus to perform the process in,according to different aspects of the invention as defined by theappended independent patent claims.

The master electrode and the substrate are put in close contact, wherelocal etching/plating cells are formed in the open or closed cavitiesbetween the master electrode and the substrate. A setup with an internalcounter electrode surface inside each local electrochemical etch orplating cell, each defined by the walls of an insulating pattern layer,enables a uniform current density distribution independent of thepattern. To enable the internal counter electrode principle of ECPR inclosed cavity electrochemical micro- and nano cells, predeposition ofsoluble anode material inside the cavities in the master electrode isbeing done prior to ECPR plating, and during ECPR etching electroplatingof excess ions in the electrolyte created from substrate etching isbeing done. This results in uniform current density distribution ofECPR, independent of any pattern applied, solves the above-mentioneddrawbacks associated with the prior art, namely different depositionspeed depending on the pattern that is plated. Moreover ECPR eliminatesthe need for a subsequent planarization, since deposited structuresalready have the same height when being plated with the ECPR method.ECPR also solves the problems with limitations in maximum aspect ratioof structures deposited in each plating cycle and reliability problemsassociated with prior art. Furthermore, when plating alloys, ECPR alsosolves the above-mentioned problem of different material composition ofdifferent structures depending on the pattern surrounding eachstructure. Thus the object of the invention is met. Another advantage ofthe ECPR method, when used for etching, is that it enables a high andwell controlled anisotropic etch profile, etch rate and surfacefinishing and uniformity, a possibility of accurate process control,minimised undercut, environmentally friendly process (since electrolyticor very diluted etchants is used) and low costs.

Another object is to design the master electrode, which is used in theECPR method.

This object is met by integrating a counter electrode and patterndefining structures of an electrochemical etching/plating cell into onedevice, the master electrode. This master electrode will operate both ascounter electrode and pattern master in the local etching/plating cellused in the ECPR method. The substrate, the sample on which the patternis to be etched or plated on, operates as a working electrode in theetching/plating cell used in the ECPR method.

By using this master electrode combined with the ECPR method, severalreplicas can be produced in conducting materials by electrochemicalmaterial removal or addition inside each local electrochemical micro- ornano-cell defined by the master electrode.

Further objects and advantages of the present invention will be obviousto a person skilled in the art from reading the detailed descriptionbelow of preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described more closely below by way of examplesand with reference to the enclosed drawings. In the drawings:

FIG. 1 is a sectional view of an etching cell used for conventionalelectrochemical etching.

FIGS. 2 a to 2 f are sectional views, which illustrate one of thefabrication processes of a master electrode, according to the presentinvention, based on open local electrochemical cells.

FIG. 3 is a sectional view of an etching/plating cell, according to thepresent invention.

FIG. 4 a is a sectional view of an etching cell, where the masterelectrode and the substrate are compressed and closed local etchingcells are formed, according to the present invention.

FIG. 4 b is a sectional view of an etch cell, where the pattern has beenetched on the substrate, according to the present invention.

FIG. 5 a is a sectional view of a plating cell, where the masterelectrode and substrate are compressed and closed local plating cellsare formed, according to the present invention.

FIG. 5 b is a sectional view of a plating cell, where the pattern isreplicated on the substrate, according to the present invention.

FIG. 6 is a flowsheet of a microfabrication process, with aphotolithography process.

FIG. 7 is a flowsheet of the ECPR process, according to the presentinvention.

FIG. 8 is a sectional view of a principal apparatus used for singlesided etching/plating with the ECPR method, according to the presentinvention.

FIG. 9 a is a side view of an example of another apparatus used foretching/plating with the ECPR method, according to the presentinvention.

FIG. 9 b is an end view of the same apparatus that is shown in FIG. 9 a.

FIGS. 10 a to 10 h are sectional views of different exemplarycombinations of designs and materials of a master electrode, accordingto the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A master electrode 8 of the present invention operates both as a counterelectrode 1 and a pattern defining master, and a substrate 9 operates asa working electrode 2 in an etching/plating cell, which is shown in FIG.3, used in the ECPR process, according to the present invention.

Further on in the description an exemplary etching or plating process ismentioned, but it should be noted that it is obvious to a man skill inthe art that it also concerns and applies correspondingly to therespective plating or etching process.

Master Electrode

The purpose of the master electrode 8 is to provide a well definedpredeposited anode material electrical connection to all local platingcells 14 formed when compressing the master electrode 8 and thesubstrate 9 and, at the same time, to provide electrical insulation tothe areas where electrochemical action is undesired, i.e. at the contactareas between an insulating pattern layer 3 and the substrate 9. Toenable a well-defined pattern transfer, even for relatively roughsubstrate surfaces, a conformable behaviour is needed, both globallyover the entire substrate surface and locally at each insulatingstructure of the pattern layer in contact with the substrate surface.This is satisfied by a flexible behaviour of the entire master electrodeglobally on the macro scale and a compressible elastomer layer 20, 21within the master electrode construction on the local micro scale.

The insulating pattern layer 3 is fabricated by using an electricallyinsulating material that is chemically inert in the electrolytes thatare used, enables high aspect ratio structures and is easily patternedusing i.e. UV, X-ray, electron beam, laser or etching/plating combinedwith an insulating process. Examples of insulating materials, which maybe used are polyimide, SU-8, SC 100, MRL 6000, ED-resist and Teflonmaterials. In another embodiment the insulating portions are made byanodising a conducting material, e.g. a metal.

The counter electrode 1 comprises a conducting electrode layer 1′.Alternatively, the conducting electrode layer may also comprise aflexible conducting foil 1″, a solid metal sheet or a thin conductinglayer on a mechanical support layer 23. When the conducting electrodelayers 1′, 1″ are deposited on a mechanical support layer 23 or anelastomer layer 21 with a very high surface uniformity, the two featuresplanarity and high surface uniformity are combined. Crucial materialcharacteristics for the conducting electrode layer 1′, 1″ are highconductivity, chemically inertness in the electrolytes used, good seedlayers for electrochemical material deposition and suitable methods fordepositing or in other ways incorporating the layer into the integratedmaster electrode construction. A non-limiting list of examples ofconducting electrode layer 1′, 1″ materials used comprises stainlesssteel, platinum, palladium, titanium, gold, graphite, chromium,aluminium and nickel.

According to an embodiment, the master electrode is manufactured byusing a conventional microfabrication method, which is illustrated inFIG. 6. The different embodiments of master electrodes used for ECPRprocessing are described in FIGS. 10 a-10 h. All different electrodelayer 1′, 1″ embodiments may be combined with all different combinationsof insulating pattern layer 3, flexible elastomer layer 20, 21,mechanical support layer 23 and intermediate metal layers 22. All theseconfigurations may be used for both an open cavity concept and a closedcavity concept. These concepts will be explained further on in thepresent document.

Master electrodes for the open cavity configuration may be fabricatedusing the method described below.

The master electrode used for open cavity configuration is fabricated intwo major steps. In the first step the counter electrode layer 1 isshaped and prepared to meet the different requirements stipulated ascrucial for successful ECPR processing. After meeting these requirementsan insulating pattern layer 3 is deposited and patterned on the counterelectrode layer 1.

In the preferred embodiment titanium has been chosen as a masterelectrode material since it is inert in the electrolytes being used.Furthermore, anodising can form a dense insulating outer layer of TiO₂at the contact areas. It is possible to use other materials as well,which has been mentioned above.

Since the master electrode 8 is in contact with the working electrode 2,some parts of the master electrode have to be made of an insulatingmaterial, an insulating pattern layer 3 on the contact side, the masterside 11. The insulating pattern layer 3 prevents the areas where etchingis undesired from etchant contact.

All the manufacturing steps of the master electrode 8 may be carried outwith conventional microfabrication processes, known from the prior art,wherein characteristic steps are shown in FIG. 6.

Accordingly, the master electrode 8 will be fabricated out of twotitanium foil layers 16, as stated before, which is shown in FIGS. 2 ato 2 e, with a sacrificial photo-resist layer 17 inbetween, to formgas/electrolyte transport channels. An example of how the fabrication ofthis master electrode may be performed is as follows:

-   -   1. The starting material, the sample in FIG. 6, is a 4 μm        Ti-foil layer 16. A 1 μm sacrificial photo-resist layer 17 is        electrochemical deposited, as shown in FIG. 2 a. To form fluidic        channels, the resist forms square with 4 μm width, separated        with 1 μm resist lines, as shown in FIG. 2 b. A second Ti-foil        layer 16, 3 μm, is deposited on top of the sacrificial resist        layer 17, as shown in FIG. 2 c.    -   2. Both long sides of the “sandwich”, which are shown in FIG. 2        c, are coated with ED-resist 18, as shown in FIG. 2 d. The        master side 11 is patterned with desired master pattern and the        outer side 10 is patterned with 1 μm holes, according to the        pattern definition process shown in FIG. 6.    -   3. Double-sided electrochemical etching is performed, according        to the pattern transferring process shown in FIG. 6. The outer        side 10 is etched to the sacrificial resist layer and the master        side 11 is etched to a depth of 3 μm, saving 1 μm for gas traps.        A new layer of ED resist is deposited. The contact areas are        exposed and developed. The contact areas are anodised and        isolating TiO₂ is formed, as shown in FIG. 2 e.    -   4. The photo-resist is stripped thoroughly in alkaline solution        to dissolve outer layers and sacrificial layer, as shown in FIG.        2 f.

All fabrication steps for the outer side 10 of the master electrode 8are standardised and do not depend on what kind of master structure thatis used. Universal standard masks may be used. Only the masks for themaster-side 11 have to be selected for every specific master structure.The master electrode is ready to be mounted in an etching cell.

The fabrication of a closed cavity master electrode may be performed inthe same way as the above described fabrication process of the opencavity master electrode except for the sacrificial resist layer. Severalcombinations of material are shown in fig 10 a to 10 h.

A very important part of the ECPR process is to use a suitableinsulating layer. One of many benefits of the process is that it wouldno longer be needed to apply a resist on each sample but instead theresist would be out on a reusable master. For this to be a benefit it ofcourse requires that the resist withstand several process cycles.Besides that, the resist also governs how small structures that can bemade, what volume electrolyte to sample depth ratio one can have andalso, how easy it is to keep all structures in contact with the sample.Electro-deposited photo-resist, ED resist, which is often used forlithography processes, is suitable for these etching processes as it canbe deposited with very precise thickness control.

The embodiments of the master electrode according to the presentinvention are in no way limited to the examplary constructions anddesign shown neither in FIGS. 2 a-2 i, or 10 a-10 h, nor to thematerials listed as suitable in the description above.

Substrate

Any electrically conductive material durable to electrochemicalstresses, e.g. copper, may be used as substrate material.

Electrolyte

The electrolyte composition is crucial in controlling an electrochemicalprocess and its different features. Conductivity, ion mobility, ionicatmosphere, relaxation, migration, diffusion and transport numbers areimportant concepts.

When an electrolytic etchant is used there is no or less chemicaletching and the negative influences will be negligible on the replicatedstructures. The existence of chemical etching depends on if there is achemical oxidation agent present in the electrolyte solution.

One important issue that the electrolyte has to take care of is tooptimise a mass-transport of electro-active ions in localelectrochemical cells, which has to occur to achieve an optimisedECPR-process. The optimisation of the electrolyte to cause an optimisedmass-transport is described below, after the description of theECPR-process.

Reducing components, e.g. metal ions, could be added to the electrolytesolution if one wants to prevent deposition of substrate material and tocause an etch process to stop in a natural way. When reducing componentsare added the reduction process will take place in the electrolyte andthere will be a natural ending of the etching process when there is abalance between the reduction components and the deposited components.

ECPR Process

The substrate 9 and the master electrode 8 are put together in closecontact and form an etching cell, as shown in FIG. 4 a.

They will be mounted in an apparatus where the ECPR process will takeplace. This apparatus will be described in more detail below. One of itsmain issues is to keep the electrodes in exact place once they are putin contact and to supply them with a conformable contact.

The insulating pattern layer 3 defines the distance between the counterelectrode 1 part of the master electrode and the substrate 9. Thanks tothe fact that the distance is short and precise all over the surface itsolves the problems with non-uniform current density distribution andnon-etched areas. It also minimises the resistive losses from chargetransfer in the electrolyte.

The structure is replicated on the substrate 9 because the field andmotion of the ions in the etching/plating solution is controlled invertical direction by the master electrode 8.

Since the master electrode 8 and the substrate 9 are in close contact,closed or open cavities, local etching cells 12, are provided betweenthe electrode surfaces. If the cavities are open or closed depends onhow master electrode 8, that is used, is constructed, with or without asacrificial resist layer 17. The cavities are considered to be closedfurther in the document. These, very small and well-controlled, spacesbetween the electrodes provide an effective etching with high precision.Every local etching cell 12 has a surface on the master electrode 8,which corresponds to a surface on the substrate 9 which is to be etchedaway and thereby avoiding the problems with fluctuating current densitydistribution in the vicinity of large insulating areas with adjacentsmall structures.

According to the invention, an ECPR method for etching selected parts ofa surface defined by the master electrode, which was described above,has thus been provided.

FIGS. 3, 4 a and 4 b show the different steps in the ECPR etchingprocess, according to the present invention. The steps are as follows:

-   -   1. The master electrode 8 and the substrate 9, are immersed into        an electrolyte solution 6, which will be described later, as        shown in FIG. 3.    -   2. They are compressed and an etching cell with local etching        cells 12, filled with electrolyte solution 6, is formed. This is        shown in FIG. 4 a. It is also possible to apply the electrolyte        solution as a very thin layer of liquid on one of the surfaces        before the electrodes are compressed, e.g. by dipping the        surfaces into the electrolyte solution before the compress        procedure, or to supply the electrolyte solution to the etching        cell, after compressing the electrodes, through the layer on the        outer side 10 in the master electrode 8.    -   3. An external pulsed voltage with or without additional        ultrasound is applied over the etching cell, where the substrate        9 becomes the anode and the master electrode 8 becomes the        cathode.    -   4. FIG. 4 b shows how the pattern 3, which is defined by the        master electrode 8, is replicated on the substrate 9. The        material that has been etched away has been deposited on the        master electrode 8, a deposit material 13, all inside each local        electrochemical cell.    -   5. Since some of the substrate material that is etched from the        anode is deposited in the structure on the master electrode 8 it        will eventually be filled with substrate material, deposit        material 13, and therefore it is essential to have an easy way        to clean the master electrode. After a number of etching cycles,        a cleaning process is normally performed. The deposit material        13 is etched away from the master electrode 8.

FIGS. 5 a and 5 b shows the different steps in the ECPR plating process,according to the present invention. The plating process is almost thesame as the etching process except the following steps:

-   -   1. Before the electrodes 8, 9 are compressed and immersed into        electrolyte solution, plating material 15 has been deposited on        the master electrode 8 in the cavities, which are defined by the        insulating pattern layer 3. When a certain height of the plating        structure has been reached will the space, formed by the local        plating cells 14 between the master electrode 8 and the        substrate 9, be filled with electrolyte solution 6, as shown in        FIG. 5 a.    -   2. The pattern, which is defined by the master electrode 8,        replicates on the substrate 9 when the external pulsed voltage        is applied over the plating cell 14, where the master electrode        8 becomes the anode and the substrate 9 becomes the cathode.        Consequently, the plating material 15, which was deposited on        the master electrode 8, has been plated on the substrate 9, as        shown in FIG. 5 b. Since all plating material, which can be        plated on the substrate, has, from the beginning, been deposited        on the master structure, the amount of plating material, which        is plated on the substrate, is controlled with high precision.

Major advantages using the ECPR process are uniform current densitydistribution in each local electrochemical cell and globally over theentire substrate independent of cell size, shape and neighbouring cellsaccording to the pattern. As mentioned in the above summary of theinvention, this solves the problems of non-uniform height of platedstructures, the problem with non-uniform material composition whenplating alloys, and eliminates the need for a subsequent planarizationprocess. It also enables deposition of structures with high aspectratio, i.e. height/width ratio, and a highly reliable process for largescale production.

An optimised mass-transport of electro-active ions in these cells has tooccur to achieve an optimised ECPR-process. The mass-transfer, withtransport of material from one location in solution to another location,arises from differences in electrical or chemical potential at twolocations, or from movement of a volume element of solution. There arethree modes of mass-transfer, migration, diffusion and convection. Forthin-layer electrochemical cells, as is in this case, there is a muchlarger A/V ratio than for regular macroscopic cells. The high A/V ratioimplies large frictional forces per unit volume, making all electrolytevolumes to stagnant layers. This means no forced convective masstransfer occurs, except when using ultrasound, leaving only thediffusion and migration mechanisms to exert the material transport. Thisconcerns the closed cavity master electrode. In the open cavity masterelectrode there is a micro-convection because of the sacrificial resistlayer, where the channels in the layer allow a micro-convectionmechanism.

Following actions is made to optimise the mass-transport:

1. Electrolyte Solution

The parameters that were adjusted in the solution were the pH-value andthe electro-active species/supporting electrolyte ratio.

In one embodiment acid copper electrolyte was used as electrolytesolution. The pH-value was changed by adding either H₂SO₄ or dilutedNaOH. Several experiments were made to establish which pH-value was thebest. It was settled, in this embodiment, that a pH-value of 2 to 5 wassatisfying.

No or less supporting electrolyte in combination with a higherconcentration of electro-active species, compared to standardelectrolytes, also improves the mass-transport. A concentration ofelectro-active species of 10 to 1200 mM is preferred.

The ECPR process involves both electrochemical etching andelectro-deposition at the same time. Electro-deposition is the reversedelectrochemical etching process, where ions from the electrolyte isreduced and deposited on the cathode. The same conditions apply and thesame parameters control the two processes. With conventionalelectroplating processes there is a tendency to obtain a higherdeposition rate at the top of a cavity, than at the bottom, when thehigh aspect ration structures are to be filled. This might result invoids, affecting the mechanical and electrical properties of themicrostructure in a negative way. The geometry of the localelectrochemical cell and the use of additives are solutions to enable“bottom-up-filling” without any voids. Additives are added to give theelectrolyte a sufficiently controlled electro-deposition. Additives areoften used in plating processes to make the plating even. It containsseveral active components but predominantly it prevents the forming ofpillars by being attracted to and covered high current density areas assoon as the pillars start forming. This turned out to be a key to theproblem and as soon as it was used a clean and solid substrate materialwas formed on the cathode. Several commercial systems have been testedwith satisfactory results. Coveted additives are wetting agents, whichlowers the surface tension, accelerators, which are molecules thatlocally increases current density where they absorb, suppressors, whichare polymers which tend to form current-suppressing film on the entiresubstrate surface (could sometimes use chloride as co-suppressor) andlevelers, which are current suppressing molecules with mass transferdependent distribution.

To avoid a far too high concentration of electro-active species at theanode, which give a local saturated compound and deposition of solidsalt, the counter-ions are exchanged to ones, which provide a highersolubility product. Further, a sequestering agent could be added, e.g.EDTA, to dissolve more metal ions without causing any furtherprecipitation.

2. Voltage

Pulsed-voltage was chosen because it enhances mass transfer and disturbsthe formation of blocking layers at the electrode-solution interface.Tests were made to determine what kind of frequencies, duty cycles andpotentials to use. Both periodic pulse reverse voltage (PPR) and complexwaveforms have been used with success. Frequencies of 2 to 20 kHz havebeen tested with satisfactory results but also higher frequencies arepossible. In the described embodiment the frequency of 5 kHz ispreferred. The potential is from 0 to 10 V.

3. Ultrasound

Ultrasound may be used together with pulsed voltage to enhance themass-transport by micro-convection.

A machine solution to exert the actions described in this document is acrucial part of the invention. The purpose of the machine is to compressthe two electrode surfaces, the master electrode and the substrate, tocreate the micro/nano cavities where the local electrochemical cells areformed. To enable conformable surfaces in both micro/nano- and macroscale, flexible layers in the machine, for macro scale conformablebehaviour and plane parallelism, are combined with flexible layerswithin the master electrode, which enables micro- and nano scaleconformable behaviour. In this way both bent and dented substrates witha rather high surface roughness can be used for ECPR processing.

Before compressing the electrodes 8, 9 to create the local etching cells12, all gas has to be evacuated from the solution and from thesolid/liquid interface between the master electrode 8/electrolyte 6 andelectrolyte 6/the substrate 9. In one embodiment this is done using avacuum system and in another using ultrasound. The two gas bubbleelimination methods can also be combined. Evacuated gas and electrolytehas been taken care of by a buffer volume connected between a reactionchamber and a vacuum system.

To enable the ECPR process, both master electrode 8 and substrate 9 haveto be electrically contacted in the same machine solution. This has beendone with outer side 10 contacting on the master electrode 8 and frontside, the contacting side, contacting on the substrate 9. The inventionis however in no way depending on this configuration.

There are two main machine embodiments to perform the desired actionsfor ECPR processing.

The first embodiment, which is shown in FIG. 8, is based on a membranesolution where a pressurised membrane 24 is expanded against the masterelectrode 8 or the substrate 9. The medium 19 inside the pressure volumecan be both gas and liquid. Gas bubbles are eliminated by a combinationof ultrasound and vacuum, or just using ultrasound. In this embodimentelectrical contact to the master electrode 8 is provided from the outerside 10, i.e. from the membrane 24 and contact to the substrate 9 fromthe front side. Plane parallelism is ensured by the nature of theexpanding membrane, applying an even pressure in a conformable way. Bothflexible and rigid master electrodes and substrates can be used in thisembodiment.

The second embodiment is based on a cylinder, which is shown in FIG. 9,containing a moveable piston, not shown in the figure. The entire systemis confined. Pressure is applied to compress the two electrodes 8,9pneumatically using a combination of vacuum and overpressure orhydraulically using a hydraulic piston or mechanically using a screw.Gas bubbles are eliminated by a combination of ultrasound and vacuum. Inthis embodiment electrical contact 26 to the master electrode isprovided from the outer side 10 and contact to the substrate 25 from thefront side using conducting movable rods. Plane parallelism is ensuredby two flexible elastomer layers between the sample and the piston, onebeing more compressible than the other is. These elastomer layers canalso be placed behind the master electrode 8, i.e. between masterelectrode and cylinder wall. Both flexible and rigid master electrodesand substrates can be used in this embodiment.

The invention is in no way limited to the embodiments illustrated anddescribed above, and several modifications are feasible within the scopeof protection as defined in the appended claims.

1. An electrochemical pattern replication method for production ofmicro- or nano-structures of an electrically conductive material on asubstrate (9), whereby an etching or plating pattern is replicated,defined by an electrically insulating patterned material, said methodcomprising using an electrochemical process for transferring saidpattern onto the substrate (9), said electrochemical process comprisingdissolving a material at an anodic surface and depositing the materialat a cathodic surface, characterized by placing a master electrode (8)in close contact with the substrate (9) so that the pattern is definedusing the master electrode (8), and said dissolving and depositing ofmaterial being performed in local etching or plating cells (12,14) beingformed in closed or open cavities, delimited by an insulating patternlayer (3) of the master electrode (8), and the substrate (9), the masterelectrode (8) being the anodic surface and the substrate being thecathodic surface and the material being dissolved being a predepositedmaterial on the mister electrode in the local plating cells (14), or thesubstrate (9) being said anodic surface and the master electrode beingsaid cathodic surface and said cavities being local etching cells (12).2. The method according to claim 1, characterized by the steps ofcharging the cavities on the master electrode (8) with an electrolytesolution (6); compressing the substrate (9) and the master electrode (8)in close contact, thereby creating the local etching cells (12) chargedwith the electrolyte solution (6); and connecting an external voltagebetween the substrate (9), which is the anode, and the master electrode(8), which is the cathode.
 3. The method according to claim 1,characterized by the steps of predepositing a plating material (15) inthe cavities on the master electrode (8) and charging them with anelectrolyte solution (6); compressing the substrate (9) and the masterelectrode (8) in close contact, thereby creating the local plating cells(14) charged with the electrolyte solution (6); and connecting anexternal voltage between the substrate (9), which is the cathode, andthe master electrode (8), which is the anode.
 4. The method according toany of claims 1 to 3, characterized by a distance between the masterelectrode (8) and the substrate (9) being determined by the thickness ofthe insulating pattern layer (3).
 5. The method according to claim 2,characterized by a further step of cleaning of the master electrode (8),after a number of etching cycles.
 6. The method according to claim 5,characterized by the cleaning step being an etching process, wheredeposit material (13) on the master electrode is etched away.
 7. Themethod according to any of the preceding claims, characterized by usingpulsed voltage applied between the master electrode (8) and thesubstrate (9).
 8. The method according to claim 7, characterized in thatthe frequency is in the range of 2 to 20 kHz.
 9. The method according toclaim 7, characterized in theft the frequency is 5 kHz.
 10. The methodaccording to any of claims 7 to 9, characterized in that the pulsedvoltage is a periodic pulse reverse voltage.
 11. The method according toany of claims 7 to 10, characterized in that the pulsed voltage hascomplex waveforms.
 12. The method according to claim 2 or 3,characterized in that the electrolyte solution (6) has no or lesssupporting electrolyte and a high concentration of electro activespecies and/or no chemical oxidation agent.
 13. The method according toclaim 2 or 3, characterized in that counter ions in the electrolytesolution (6) is exchanged to ones which provide higher solubility. 14.The method according to claim 2 or 3, characterized in that aconcentration of electro active ions of 10 to 1200 mM in the electrolytesolution (6) is used and/or that a sequestering agent is used.
 15. Themethod according to claim 14, characterized in that sequestering agentis EDTA.
 16. The method according to claim 2 or 3 characterized in thatan additive system is used in the electrolyte solution (6), comprisingwetting agents, accelerators, suppressors and/or levelers.
 17. Themethod according to claim 2 or 3, characterized in that the electrolytesolution (6) comprises acid copper and the electrolyte (6) has a pHvalue between 2 and
 5. 18. The method according to any of claims 12 to17, characterized using said electrolyte solution (6) being an optimisedelectrolyte in the local etching cells (12) or the local plating cells(14).
 19. An electrode suitable for an etching or plating process,characterized in that a counter electrode (1) and a pattern definingstructure of an electro chemical etching or plating cell are integratedinto a master electrode (8), wherein the counter electrode (1) is aconducting electrode layer (1′) or a flexible conducting foil (1″), andthe pattern defining structure is an insulating pattern layer (3) beingapplied on said counter electrode (1).
 20. The electrode according toclaim 19, characterized in that the counter electrode (1) is inert. 21.The electrode according to claim 19 or 20 characterized in that aflexible elastomer layer (20) is applied on the insulating pattern layer(3).
 22. The electrode according to any of claims 19 to 21 characterizedin that the counter electrode (1) is applied on a mechanical supportlayer (23).
 23. The electrode according to claim 22 characterized inthat a conductive elastomer layer (21) is applied between the counterelectrode (1) and the mechanical support layer (23).
 24. The electrodeaccording to claim 21 or 22 characterized in that an intermediate metallayer (22) is applied between the insulating pattern layer (3) and theflexible elastomer layer (20).
 25. The electrode according to any claim19 characterized in that the flexible conducting foil (1″) is made oftitanium.
 26. The electrode according to claim 24 or 25 characterized inthat the master electrode (8) comprises two counter electrodes (1) witha sacrificial photo-resist layer (17) applied in between and thatcontact parts of the master electrode, structures of the insulatingpattern layer (3), are electrochemically anodised to form an isolatinglayer.
 27. An apparatus for performing the method according to claim 1,characterized by comprising a master electrode (8) and means forcreating conformable contact between the master electrode (8) and asubstrate (9).
 28. The apparatus according to claim 27, characterized inthat said means are one or more elastomer layers in the master electrodeconstruction.
 29. The apparatus according to claims 27 or 28,characterized in that said means are combined with a conformablemembrane.
 30. The apparatus according to claim 27, characterized in thatthere are conducting means for electrical connection to the masterelectrode (8) on an outer side (10) and electrical connection to thesubstrate (9) on a contact side (11).
 31. The apparatus according toclaim 27, characterized in that the master electrode (8) is fixed in theapparatus by an applied vacuum.
 32. The apparatus according to claim 30,characterized in that said conducting means for electrical connectionsis a conducting piece (28) applied on the outer side (10) of the masterelectrode (8).
 33. The apparatus according to any of claims 27 to 32,characterized in that the master electrode is fixed in the apparatus bya pressure against a conducting piece, said pressure exerted by theconformable membrane and/or a piston.
 34. The apparatus according toclaim 33, characterized in that said pressure when applied with theconformable membrane is combined with a reservoir containing gas orliquid.
 35. The apparatus according to any of claims 27 to 34,characterized in that gas bubbles are eliminated from in electrolytesolution (6) and/or the reservoir by use of an externally appliedvacuum, ultrasound or a combination of vacuum and ultrasound.